Alkyne-containing Cyanoethyl-N,N-diisopropyl Phosphoramidites (CEPs) are used to synthesize oligonucleotides by automated standard protocols. The resulting Alkyne-modified oligonucleotides can subsequently be labeled with Azides of fluorescent dyes or Azides of Biotin dyes by a Cu(I)-catalyzed Azide-Alkyne Click Chemistry reaction (CuAAC). This allows the synthesis of highly-modified DNA strands carrying multiple labels in a density that is not achieved by classic labeling techniques.